The invention relates to a device for safeguarding an uninterruptible power supply of a magnet bearing in the event of failure of an electrical supply voltage.
The shafts of rapidly rotating motors are increasingly often mounted on contactless magnet bearings instead of conventional sliding or rolling bearings. A magnet bearing in this case always needs to be actively regulated.
In motors, in particular in motors of machine tools, production machines and/or robots, magnet bearings are used to an increasing extent for bearing a motor shaft or any desired other shaft which is driven by a motor. Increasingly often magnet bearings are used in particular for bearing spindles.
However, in contrast to conventional rolling body bearings, magnet bearings need to be continuously supplied with electrical energy in order to ensure a bearing arrangement in accordance with regulations. If the supply voltage of the magnet bearing fails, for example as a result of an electrical failure of the power supply system, not only will the motor run down, but also the functionality of the magnet bearing will no longer be provided. In order to avoid damage to the magnet bearing, the shaft and/or other components in the event of failure of the supply voltage of the magnet bearing when the motor is still rotating, in the case of conventional magnet bearings so-called emergency operation conditions are implemented mechanically which for a limited number of failures of the supply voltage of the magnet bearing still ensure an emergency bearing arrangement without the magnet bearing, the shaft or other components being damaged. However, applications of magnet bearings in fields with insufficiently stable electrical power supply systems are still problematic. The maximum permissible number of emergency operation rundowns of the magnet bearing is then quickly reached, with the result that the abovementioned components need to be replaced even after a relatively short period of time. This replacement is generally time-consuming and associated with high costs.
In the case of conventional machine tools, magnet bearing systems are known in which the drive units of the magnet bearing are supplied with electrical energy by the same converter DC-link circuit to which the remaining drive units of the machine tool are also connected. In the event of a power failure, the DC-link circuit can then be maintained in terms of energy from the energy of the rotating spindle. As a result, the spindle (rotating rotor) is braked and the magnet bearing at the same time retains its functionality without a so-called uninterruptible power supply system, for example in the form of a battery-buffered supply, being necessary for this purpose.
For example, the German laid-open specification DE 43 06 307 A1 has disclosed a method for preventing damage to numerically faulty machines in the event of failure of the power supply system. This document provides that the kinetic energy of a main spindle drive is fed back in regulated form to the DC-link circuit in the event of failure of the power supply system and program-controlled emergency retraction of the tool spindle is implemented.
Drive units for magnet bearings generally function with a DC-link circuit voltage of from 150V to 750V. This voltage range is technically referred to as “low voltage”. Particularly high-power motors are often supplied with substantially higher voltages (for example 3 kV). If such a motor has a magnet bearing arrangement, the braking energy can no longer be transmitted directly from the DC-link circuit of the converter provided for driving the motor into the DC-link circuit of the converter of the drive unit for the magnet bearing.
Therefore, in particular in such cases, the uninterruptible power supply systems mentioned already at the outset are often used for safeguarding an uninterruptible power supply of the magnet bearing in the event of failure of the electrical supply voltage. An uninterruptible power supply system maintains the functionality of the magnet bearing arrangement, for example of a shaft, until the rotating shaft is braked to a sufficient extent and no damage or wear occurs during mounting in the emergency bearing arrangement.
However, uninterruptible power supply systems have a plurality of disadvantages:                Uninterruptible power supply systems represent a considerable cost factor in the case of magnet bearings.        Uninterruptible power supply systems take up a considerable amount of physical space.        In order to ensure the functionality of the batteries of an uninterruptible power supply system, certain environmental conditions such as temperature, air humidity etc. need to be adhered to.        The batteries need to be tested and maintained regularly.        